Differential signal communication systems are in widespread use. For example, RS-485 is a well known serial digital communication system that uses balanced differential signals for communicating with computers and other devices. RS-485 allows multiple devices to communicate at half-duplex on a single pair of wires, plus a ground wire, over long distances. Both the length of the network and the number of nodes can easily be extended using a variety of different repeater products that are readily available. The properties of differential signals provide high noise immunity and long distance capabilities.
RS-485 is the most versatile communication standard in the standard series defined by the EIA, as it performs well for connecting data terminal equipment (DTE) directly without the need of modems, for connecting several DTE's in a network structure, for communicating over long distances, and for communicating at fast communication rates. RS-485 is currently a widely used communication interface in data acquisition and control applications where multiple nodes communicate with each other. RS-485 signals are floating with each signal being transmitted over a S+ line and a S− line. The RS-485 receiver compares the voltage difference between the two lines, rather than the absolute voltage level on a single line.
RS-485 interfaces are often preferred for data acquisition and control applications because RS-485 is capable of internetworking multiple transmitters and receivers in the same network. High-resistance RS-485 inputs allow a large number of nodes to be used, and RS-485 repeaters can be used to increase the number of nodes even more.